Aperiodic pulse timing system



Aug. 1947- s. c. HIGHT 2,426,216

APERIODIC PULSE TIMING SYSTEM Fi1 ed Oct. 19, 1942 4 Sheets-Sheet 5JVAVA AVA I57} I 490 a v OUTPUT WAVE I my me /72 IZ3- I75 WITHFEEDBACK.l

BALANCED INPUT (202 INVENTO/Q S. C. H/GHT A TTORNEY Patented Aug. 26,194'? inane 2,426,216 APERIODKC PULSE TIMING SYSTEM Stuart C. Hight,South Orange, N. 5., assignor to Bell Telephone Laboratories,Incorporated,

New York, N. Y., a corporation of New York Application October 19, 1942,Serial No. 462,525

(Cl. 250-l.66)

Claims.

This invention relates to timing arrangements and more particularly toarrangements for precisely determining the reflection time of pulses inpulse reflection radio object locating systems. It is directedparticularly to arrangements, commonly known as ranging units, whichreadily adapt themselves for use in that type of pulse reflection radioobject locating system in which it may be desired to emit exploratorypulses at irregular or changing periodicities as distinguished from themore usual types of pulse reflection systems which employ a fixed orinvariable and accurately determined pulsing rate. The arrangements ofthe invention can of course be employed in periodic as well as aperiodicsystems.

Pulse reflection radio object locating systems are Well known, in whichpulses are emitted at regular accurately determined intervals from ahighly directive antenna system, the antenna system being directed toexplore an area so that the emitted energy will impinge upon objects,particularly ships, aircraft, obstacles, and the like, within the areaand be reflected back to the point of observation, whereupon they arereceived and by determining the interval between the emission of pulsesand the receipt of reflections thereof from a particular object thedistance of the object from the observation point may be determined. Ithas been the customary practice to emit the exploratory pulses atregular accurately determined time intervals, the time intervalsexceeding the time required for the reflections to return from objectsat the maximum distance to be determined by the system, so that allreflections of interest will be received before the next succeedingpulse is emitted.

Such systems are usually open to the objections that their accuracyisimpaired if the pulsing rate departs from its normal rate, that if it isdesired to employ a number of such systems within a relatively limitedarea interference may be encountered, and that when used for militarypurposes the enemy may readily jam or cause interference with theindications obtained by them by directing pulses of the fixedperiodicity toward the exploratory systems.

To avoid the above-mentioned difficulties the present invention providessystems in which the interval between successive emitted pulses may, ifdesired, be varied within wide limits and at random without in the leastdiminishing the accuracy of the range or distance indications providedby the system. This is effected by employing, as a timing device, aresonant device, the device being shock-excited into vibration, or

oscillation, by the same control impulse which simultaneously, or aftera small time delay, causes the emission of an exploratory energy impulsefrom the directive transmitting antenna of the system. The ranging unitsof the invention then employ the regularly spaced oscillations of theresonant device as timing units and provide means for determiningprecisely the time, in terms of these oscillations, required for anemitted pulse to travel to a particular object and to be reflected backto the point of observation.

Naturally the timing oscillations must persist for a time interval equalto that required for reflections to be received from an object at themaximum range to be measured. Also a very short time interval forquenching the resonant device, 1. e., for restoring it to a passivestate, is required before the next successive shock-excitation isapplied.- These factors prescribe a maximum recurrence rate for theemission of exploratory pulses and any lesser rate down to that whichwill just produce satisfactory indications on the indicating mechanismemployed can be used. Between the above-indicated limits the pulsingrate may be varied at will and if desired in any irregular or randommanner without impairing the accuracy of the range indications.

Obviously, therefore, with systems employing the principles of thisinvention, no precise control of the pulsing rate of the transmitter isnecessary, adjacent friendly systems may select pulsing rates which willproduce a minimum of interference. with each other and jamming byhostile pulsing systems can be rendered very difficult by employing arandom variation of the pulsing rate;

An object of the invention is, therefore, to provide ranging units andmethods for use with pulse-reflection object locating systems, whichwill provide precise range indications and at the same time permitsubstantial variations in the rate at which exploratory pulses areemitted.

A further object is to provide ranging units suitable for use inpulse-reflection object locating-systems of variable pulsing rates.

Another object is to provide convenient means for readily minimizinginterference between pulse-reflection object locating systems employedin a common area and to' render it difficult for hostile systems in thearea to jam such systems.

Other objects will become apparent during the course of the followingdescription and in the appended claims.

7 The principles and features of the invention will be more readilyunderstood from the following detailed description of preferred forms ofranging units and apparatus therefor illustrated in the accompanyingdrawings, in which:

Fig. 1 shows in block-schematic diagram form a pulse-reflection typeobject locating system employing a ranging unit for determinin thedistance to objects from which reflections are received;

Fig. 2A illustrates, in block-schematic diagram form, one type ofranging unit of the invention;

Fig. 23 illustrates for a cycle of operation the Wave forms and the timerelations between them of the energy as it passes through the componentapparatus elements of the unit of Fig. 2A;

Fig. 3A illustrates, in block-schematic diagram form, a second type ofranging unit of the invention;

Fig, 33 illustrates for a cycle of operations the 7 wave forms and thetime relations between them of the energy as it passes through thecomponent apparatus elements of the unit of Fig. 3A;

Fig. 4A shows inelectrical schematic form, a simple start-stop circuit,with cathode feed back and an LC oscillatory circuit associatedtherewith suitable for producing the shock-ex-' cited oscillatory wavesemployed for timing in systems of the invention;

Fig. 4B illustrates the wave forms and the time relations between themof the energy as it passes through the circuit of Fig. 4A;

Fig. 5A illustrates in electrical schematic diagram form a preferredtype of phase shifter for use in ranging units'of the invention;

Fig. 5B illustrates the relative phases of the energy on the fourquadrant stators of the phase shifter of Fig. 5A;

Fig. 5A illustrates in electrical schematic diagram form a simplecircuit for generating a square-topped pulse for use as a "pedestalselector or unblocking pulse in units of the invention; V

Fig. 63 illustrates the wave forms and the time relations between themof the energy at various points in the circuit of Fig. 6A;

Fig. 7A shows in schematic diagram form a suitable step generatingcircuit for systems of the invention;

Fig. 7B illustrates the formation of the step voltage in the circuit ofFig. 7A;

Fig. 8A shows in schematic diagram form a timing circuit providing anunblocking impulse for systems of the invention; and

Fig. 83 illustrates the operation of the circuit Of Fig, 8A. I 1 t Inmore detail in the pulse-reflection object locating system of Fig. 1,adjustable oscillator 10 provides, for example, a sine wave, thefrequency of which may be varied over a wide range, the highestfrequency being such that a single cycle is completed within a timeinterval slightly greater than that required for a radio wave to traveltwice the distance to an object at the maximum range of the system. j

Energy from oscillator H3 is appliedt'o pulse generator i i, the pulsesof which energize transmitting oscillator l6. Pulse generator I 5'provides a sharp squared-top positive pulse at a particular point ofeach cycle of the sine wave supplied to it These pulses are preferablyof from 1 to 5 microseconds in duration and key the transmittingoscillator in which, thereupon, furnishes like pulses of high power toantenna IS. the latter corresponding pulses E9 of Antenna I8 is usuallydirecserving .to radiate radio Wave energy.

tive so that the direction in which it is pointed and their principlesconnected to the horizontal cathode ray oscilloscope 28. When theprecision sweep circuit 24 is employed, a

4 for maximum amplitude of reflection from a particular object willserve to indicate the direction of the object.

Reflections 33 of the emitted pulses l9 are received on antenna 32 whichis preferably sufiiciently directive to discriminate effectively againstthe direct transmission of energy from antenna i8. Alternatively, asingle antenna can be employed for both transmitting and receiving, anda suitable duplexing arrangement is then employed to isolate thetransmitter and receiver of the system from each other in accordancewith principles well known in the art. The reflections 33 are detectedand amplified in receiver 38 and when switch i3 is closed they areapplied to the vertical deflecting plates of cathode ray oscilloscope 28I The sine wave provided by oscillator ID is also applied to a secondpulse generator 28 which provides a positive pulse for each cycle of thesine wave substantially as does the pulse generator Hi. Pulse generatorsl4 and 20 may preferably be of the non-linear inductance type well knownto the art as exemplified, for example, in United States Patent2,117,752, issued May 17, 1938, to L. R. Wrathall.

The pulses of generator 25 are supplied to range unit 22 and to fullscale sweep circuit 26 as indicated. Sweep circuit 26 is preferably ofthe conventional saw-tooth wave type, its wave being synchronized with,or keyed by, the pulses provided to it as above described, and serves todeflect the ray across the scale at a uniform rate Ranging unit 22provides a range mark which is precisely timed and adjustable in timewith respect to the pulse reaching it from generator 25. Preferred formswhich ranging unit 22 may take of operation are illustrated in Figs. 2A,2B, 3A and 3B and will be described in detail hereunder.

The precisely timed range mark provided by ranging unit 22. is, whenswitch H is closed, also supplied'to the vertical deflecting plates ofcathode ray oscilloscope 28. The reflection time or distance of anyreflected pulse received by the system may be determined by adjustingranging unit 22 to align the precisely timed range mark with thereceived pulse whereupon the adiustment of the ranging unit 22 requiredis ,a measure of the time or distance.

By means of switch 25 either full scale sweep circuit 25 or precisionsweep circuit 24 may be deflecting plates of a small portion of thetotal range on each side of and including the precisely timed range markof ranging unit 22 is selected and expanded to substantially cover the.entire width of the target of the oscilloscope 28 so that ranges ofparticular interest centered about the range mark may be examined indetail and the range mark may be more accurately aligned with aparticular received reflected pulse.

In Fig. 2A there is shown in schematic block 7 diagram'form withintherectangle 38, one preferredembodiment of a. unit which can :be employedas the ranging unit22 of Fig. 1. Unit 38 is connected to the output of astarting impulse source 21 which can, for example, be the pulsegeneratorizll of Fig. 1. In the description ofthe circuit of Fig. 2A,frequent reference will be made to the curves of Fig.2B which indicatethe'forms taken by the energy at various points in passing through thecircuit of Fig. 2A.

The starting impulse source 21 provides a series of pulses '52, asindicated in curve a of .Fig. 2B. The time interval betweenthefsuccessive pulses l2 exceeds the maximum time to be measured,designated tmx in Fig. 2B, sufficiently topermit at least adequate timefor quenching the-circuit so that it will be restored to a quiescentstate before the next starting impulse occurs at time to.

Apparatus unit 40 is, as labeled, an oscillation starter and quenchingtime circuit and may have timing wave 74*. as shown in curve b of Fig.2B, although a wave approximating as closely as practicable the moreabruptly changing wave 16 :is preferable if it can be convenientlyrealized. Apparatus unit ll! will be referred to as a startstop circuitbecause its effect upon the precise oscillator 52 and the lowfrequencyoscillator 66, respectively, is that of starting and stopping theoscillations. A preferred and simple form of start-stop circuitassociated with an oscillator is shown in detail in Fig. 4A and will bedescribed at length in connection with that figure, hereinunder.

The precise oscillator 32 can, for example, preferably consist of astable, or stabilized, LC circuit comprising a coil and condenserconnected in parallel. The precision of time measurement is, as willpresently become apparent, dependent upon the accuracy of the oscillatorfrequency and consequently a dependable oscillator with stable frequencyis required.

An LC circuit may be started oscillating by a sudden discontinuity orimpulse in the current flowing in the coil. This results instantaneouslyin a damped train of waves, the degree of damping depending primarilyupon the Q, or electrical efficiency, of the LC circuit.

With many coils and condensers readily available and well-known in theart, damping is not a. severe limitation for the majority ofapplications since it has no effect upon the precision of themeasurements but only moderately limits the maximum range in timebetween to and tmax which can be employed. However, the limiting effectof damping can be entirely eliminated by the addition of positivefeedback as indicated in Fig. 2A where the output of the oscillator 42passes through amplifier lit and a portion of the amplifier output isreturned to the oscillator through feedback circuit 44.

The resulting wave train 18 of curve 0, Fig. 2B, is consequently shownwithout appreciable damping. It is, furthermore, shown with very fewcycles to avoid undue confusion in the illustration, though it is to beunderstood that in actual practice for high'precision systems, theprecise oscillator will provide a very large number of cycles during thetime interval between to and tmax. For high precision, LC circuitshaving free oscillation frequencies of 100,000 or more cycles per secondcan readily be used.

The oscillation, of course, starts at-the time to and proceeds until thetime tmax when it is quenched by restoration -of the circuit to itsquiescent state by the start-stopcircuit a pre- 11,1935, to L. A.lVIeacham, and 2,147,728 issued February 21, 'l939, to W.T. Wintringham.

Phase shifter 48 is continuously adjustable throughout a full 360degrees and will provide any desired discrete phase shift such as thatindicated by wave-80 of curve d, Fig. 2B (or any other phase relationwith respect to the waves or curve '0, Fig. 2B).

.Thephase shifter circuit must be designed to be capable of a quick riseto a stable steady state" condition. A form particularly well suited forthe purposes of this invention, is shown in detail in Fig. 5A and willbe discussed'at length hereinu'nder. 1

A control crank 52 on a shaft provides for manual-adjustment of thephase shift of phase shifter 48. The right end of shaft 50 is coupled bygears 54 :to the shaft of a second adjustable phase shifter 68, forreasons which will presently become apparent.

The output of phase shifter 48 passes through pulse generator-58 andgenerates, as indicated by curve 6 of Fig. 2B, a series of sharp pulses,the positive pulses 'being'designated by the numeral 82 and the negativepulses being designated by the numeral 84. 'These'pulses are preciselyspaced in time as they'are derived from the sine wave output of thephase shifter 48 and can be made to move to any position within thelimits of to and tmax by adjusting the phase shifter.

Any one of these pulses may be used as'a fiducial mark, and a probleminvolved in the design of suitable ranging units of the invention is thesegregation of one of these pulses from all the rest. This segregationmay be accomplished in several ways, one of which will be described inconnection with Fig. 2A and another in connection with Fig. 3A of theaccompanying drawings.

In the arrangement of Fig. 2A, the process of segregating one of theprecision pulses from the rest is'accomplished by employing theoscillator starter and quenching timer 40, previously mentioned, tooperate, simultaneously with oscillator 42, a second'shock excited butlow frequency oscillator 54, the output of which latter oscillator is asimple sine wave of curve g of Fig. 2B. The output of oscillator 54 isamplified by amplifier 66 and then passed, through phase shifter 68 topedestal generator 10 where it triggers the generation of a'pedestalpulse shown in curve a of Fig. 2B.

By the adjustment of phase shifter 68, the wave 88' of curve 1 of Fig.2B is adjusted in phase with respect to curve 86 of curve 9 of Fig. 2Band thus the pedestal-90 can be moved smoothly over the complete rangefrom the time to to imax.

As noted above, phase shifter 68 is geared to phase shifter 48, the gearratio being such that the phase'shifter 48 turns faster than the phaseshifter 68 in proportion to the ratio of the respective frequencies ofthe waves passing through them. By this arrangement one of the precisionpulses of pulse generator 58 is centered on the pedestal 90 of pedestalgenerator I and may be adjusted to any position within the completerange. This is illustrated by the addition, as curve k1, of the curves 6and 7' of Fig. 2B which results in one pulse 92 being placed upon thepedestal 9i and thus projecting higher than any of the others whereby itcan readily be separated, for example, by passing the combinationthrough a properly biased vacuum tube amplifier, the result being theselection of a single pulse 94 as shown in curve is of Fig. 2B. Thisresulting isolated precision pulse can, as previously mentioned, becaused to occur at any time between to and ftmax by appropriatelyadjusting the geared phase shifters 48 and 68.

The selected pulse may be employed directly as a fiducial mark or itmaybe applied to a separate fiducial mark generator 60 to produce somespecial form of fiducial mark such as the step 96 of curve Z of Fig. 2B.A preferred form of circuit for generator E6 is shown in schematicdiagram form in Fig. 7A and will be described in detail in connectionwith that figure.

In Fig. 3A, a second preferred embodiment, or form, which the rangingunit 22 of Fig. 1 may take for the purposes of this invention, isindicated in schematic block diagram form within rectangle Ifli and isactuated as for the arrangement of Fig. 2A by impulses from a startingimpulse source 2|, precisely as for the arrangement of Fig. 2A. In Fig.3B wave form curves illustrating the sequence of events in passingthrough the units of the arrangement of Fig. 3A are given.

In the arrangement of Fig. 3A, a starting and stopping timer circuitI0!) is employed and may be similar to timer 45 of Fig. 2A. On the leftside of the circuit, a precise oscillator, I02, an amplifier I06, afeedback circuit I84, a continuous phase shifter I03, a pulse generatorH8 and a fiducial mark generator I22 are provided as for the arrangementof Fig. 2A and for substantially identical respective purposes. I

On the right side of the circuit of Fig. 3A, however, the pedestal pulseis triggered by a resistance capacitance delay device I22, thecharacteristic of which for a particular adjustment is indicated by waveHi l of curve of Fig. 3B. The slope of curve either the capacity or theresistance of the circuit I 22. A preferred form for circuit I22 isshown in schematic diagram form in Fig. 8A and described in detailhereunder in connection with that figure. V a

When the start-stop circuit Hlil starts the precise oscillator I82, italsostarts the timing condenser 358 of Fig. 8A in circuit I22discharging through the timing resistance 3% of Fig. 8A in circuit I22and when the potential across the condenser is reduced to a certainpredetermined fraction of its initial potential, it causes a pedestal tobe generated by the pedestal generator I24 as will be described indetail hereinunder. The time required to discharge to this point isdirectly proportional to the product of the abovementioned resistanceand capacity. Varying either of these, therefore, shifts the position ofthe pedestal linearly in time so that either one can be geared to thephase shifter H28 through shaft Iii gears H4 pedestal 52% of curve g ofFig. 313 may be made to occur simultaneously with any one of theprecisely timed pulses I 36 of curve h. The resistance variationobtainable in standard apparatus I M can be adjusted by changing andshaft IIQ so that the Y parts makes the resistor the more suitableelement to vary in present applications. Details of circuit I22 will bereadily understood from the detailed description of Fig. 8A givenhereinunder.

The precisely timed pulses from generator H8 and the pedestal pulse fromgenerator I 24 are combined, as for the system of Fig. 2A, and passedthrough the fiducial mark generator I20, which can be of the same typeas generator of Fig. 2A.

In an object locating system such as that illustrated in Fig. 1 to whichthe principles discussed above are to be directly applied, distances aredetermined by measuring echo travel time. The on time tmax of the stableoscillator is related to the maximum distance Dmax, to whichmeasurements are to be made, by the following formula:

max T (1) rum:

where C=velocity of propagation of radio waves:

327,799,000 yards per second.

The precision of distance measurement is related to the frequency of theprecise high frequency oscillators and the precision of the phaseshifter by the following formula:

CAG

where The distance d covered by one turn of the phase shifter is thenphase measurement in As previously noted, the combination of a simplestart-stop circuit and high frequency precision LC oscillator suitablefor use in ranging units of the invention is shown in schematic diagramform in Fig. 4A and in Fig. 4B wave forms illustrative of the operationof the circuit of Fig. 4A are given.

The circuit of Fig. 4A operates from a positive pulse applied to theinput terminals I GI and provides instantaneous starting and rapidquenching. With an experimental circuit of this type, it was foundpossible to quench a kilocycle oscillation in'approximately 1 cycle, or10 microseconds.

Oscillation is started by the input pulse applied to terminals Nilcutting off the plate current of the vacuum tube I60 by imposing theinitial negative potential across condenser I62 on the first or controlgrid of the tube, i. e., the grid nearest the cathode, and is quenchedagain when the grid potential leaks off condenser I62 through resistanceI64 to permit the potential on this grid to return to the cut-off point.The on time is proportional to the product RC1, where R is theresistance I64 and C1 is condenser I62, and thefrequency of oscillationis dependent upon the inductance L ity C2 of condenser I80. Feedback isprovided throughcoil I16, which inductively couples the tube I60,

of coil I78 and the capacvoltage is connected across terminals I88 andI68. Condensers I10 and I14 prevent interaction of the screen orintermediate grid and plate impulses of tube I50, and resistance I'I2affords a control of the amplitude of oscillation. Condenser I82prevents direct current of the plate potential supply source of tube Ifrom appearing on the first or control grid of tube I55, i. e. the gridnearest the cathode. Tube I55 and its associated circuit elements I53,I81, 530, Iii comprise an amplifier of conventional design. The first orcontrol grid of tube I is biased sumciently negative by batteryconnection to terminals I13 and I15 to assure that the voltage swingsappearing on it from coil I18 will never drive it positive into theconductive region.

In Fig. 4B, the input pulse I84 is, as previously stated, positive andoccurs across input terminals I6I at the starting time to. The gridvoltage e occurring on the first grid of tube I50 is indicated by waveI86, representing the charging time of condenser I62 through resistanceI64, and is next shown. Curve I88 indicates the sudden drop in platecurrent IP to substantially zero when the starting impulse I82 isapplied at the time to and the recovery to normal value of plate circuitcurrent at the time tmax when the curve I86 relating to the first orcontrol grid voltage of tube I60 reaches a predetermined critical value.

The output wave with feedback is indicated by curve I90 and the efiectof damping, which effect is eliminated by the use of feedback, isindicated by comparison of the undamped curve I90 with the damped curveI92 which would obtain with no feedback.

In Fig. 5A, a continuous phase shifter circuit of the general typedescribed in the above-mentioned p'atents, 2,004,613, to L. A. Meachamand 2,147,728 to W. T. Wintringham, is indicated. For this particularuse, however, the phase shifter circuit must be designed to be capableof a quick rise to a steady state condition.

The particular circuit shown in Fig. 5A employs a quadrant-plate type ofcondenser having a single set of eccentrically mounted circular rotorplates 2I2 and four sets of stator plates of quadrant shape, the foursets of quadrant stator plates each being designated by the numeral 2I0. The set of rotor plates H2 is connected to terminal '2I8 byconductor 2I5. Input terminals 200 and 204 are balanced to ground onterminal 202 as indicated and capacities 200 and 2I6 and resistances 208and 2M serve to provide potentials in proper quadrature relationship atpoints 0 and d which are connected to stator plates 2 I 0. Curves 222,224-, 226 and 22B of Fig. 5B show the relative phases on the four setsof stator quadrant plates 2 I 0 and illustrate the absence of atransient efiect upon the sudden application of an input voltage.

In Fig. 6A a circuit suitable for use as a pedestal generator in thearrangements of Figs. 2A and 3A is illustrated and comprises a seriescondenser 232 in the input lead, a shunt resistance 234 across the inputgrid circuit of pentode vacuum tube 236 and a screen grid potentialsupply circuit comprising resistance 244 and condenser 240, and a platelead resistor 238 and supply capacity 242. A pulse 230 furnished by asource 260 to input terminals 0. as indicated by curve a of Fig. 63results in a voltage wave 252 as shown in curve b of Fig. 63 acrossresistance 234 in the control grid circuit of pentode 235. This resultsin the generation across terminals 246 and 248 gt a square pulse 254 asshown in curve a of Fig.

In Fig. 7A th'e circuit of a preferred form of step generator is shownin schematic diagram form. This circuit is designed to respond to asharp precisely timed pulse, such as pulse 04 or I50 provided by theranging circuits of Figs. 2A and 3A respectively, as described in detailabove, here represented by pulse 3I8- of Fig. 7B, and provides astep-shaped pulse such as is represented by curve 324 of Fig. 7B, aportion of which curve, more particularly the step 3'25, is preciselyplaced and sharply defined so that alignment with respect to a receivedreflected pulse in a pulse reflection object locating system may bereadily effected with a high degree of precision. Pulse M8 is invertedand may be conveniently derived from pulse 94 or I50 abovementioned, bydrawing energy from a cathode follower circuit in a manner well knownand frequently employed in the art.

In Fig. 7A terminals 262, Ziidconnect to the series condenser 260 andthe shunt resistance 261, the time constant of which provides abroadening effect 322 upon pulse 3I8, similar to that illustrated incurve 320 of Fig. 7B. This results from the fact that the voltage acrossresistance 261 appears in the control grid-cathode circuit of pentode214. Curve 320 is the voltage appearing in the plate circuit of pentode2M and is in turn impressed upon the control grid-cathode circuit ofpentode 300 and the broadening process is repeated so that in the platecircuit of pentode 300 the desired step-shaped pulse represented bycurve 320 of Fig. 7B is obtained. The step output whose form is as shownin curve 324 abovementioned may be obtained across the terminals 3I'2, 3I4.

In Fig. 8A a preferred embodiment of the RC delay circuit- I22 of Fig.3A is shown in schematic diagram form. A sharp pulse such as 350 isimpressed upon the input terminals 352, 354. The operation of thecircuit is as follows:

Vacuum tube 352 contains two diode rectifiers through which condensers356 and 358 are charged to the peak potential of pulse 350. Thedischarge path for condenser 356 is given a fixed long time constant bymaking resistances 304 and 360 large. The time constant should be longenough that an inappreciable loss of charge occurs during one normaloperational cycle. Curve 3I8 of Fig. 83 illustrates this effect, theamplitude 310 from zero line 315 being substantially equal to that ofthe original pulse 350.

The discharge path for condenser 358 however is through variableresistance or potentiometer 500 having a control member 353 so the rateof discharge is adjustable. Curve 312 shows the rate of discharge forone particular setting of resistor 350 and illustrates its return to thezero line all in a relatively shorter time. On the output, terminal 358is normally positive relative to 336 until pulse 350 occurs whence thepotential of 388 drops to a negative value relative to terminal 3'10 asindicated in curve 382 the proportionality of potentials above and belowthe zero line 380 being determined by resistors 334 and 306. For theparticular setting of variable resistance 350 the outputpotential-passes through Zero line 380 in time T (382). For any othersetting of resistance see the time of passing through zero would bediiierent as it is directly proportional to resistance and capacitance352.

From the above it is clear that the output voltage across terminals 358,Slit passes through zero when condenser 358 discharges through theeffective portion of potentiometer 350 to half produce a sharp positivepulse at value and that the time interval between the impressing ofpulse 350 upon the input terminals 352, 354 and recovery to zero isdirectly proportional to the product of the capacity of condenser 353and the portion of potentiometer 359, which is effective in the circuit.The control of the potentiometer 369 can therefore be connected throughshafts H6 and H and gears H4 to phase shifter I08 of Fig, 3A and thepedestal pulse 145 of curve 9 of Fig. 3B may be synchronized with anyparticular one of the precisely timed pulses I36, such as I48, forexample, so that it may operate the fiducial mark generator I asdescribed above.

The above embodiments illustrate preferred applications of theprinciples of the invention. They are, however, representative only andnumerous similar and equivalent arrangements may readily be devised bythose skilled in the art in the light of the teachings of thisspecification. The scope of the invention is defined in the followingclaims.

What is claimed is:

1. In a pulse reflection distance determining system, a timingarrangement comprising the combination of an oscillatory device adaptedfor shock excitation and substantial instantaneous quenching andproviding a high frequency electrical wave upon excitation, a firstelectrical circuit cooperatively coupled with said oscillatory device toprovide shock excitation of said device at instants intimatelyassociated with the beginnings of the time interval to be measured andallowing said excitation to continue throughout intervals exceeding thelongest time intervals to be measured and to quench said devicefollowing each excitation after an interval which also exceeds thelongest time intervals to be measured but is less than the intervalbetween successive shock excitations, a second electrical circuitcooperatively coupled with the oscillatory device to a predeterminedpoint in each cycle of the wave generated by the oscillatory device, anoutput device normally unresponsive to the pulses generated by saidsecond circuit, a third electrical circuit cooperatively connected withsaid first and said second circuits and said output device, said thirdcircuit providing said output device with a positive impulse which whencombined with a particular positive pulse from said second circuitrenders said output device responsive to pass said particular pulseonly, and adjutable electrical timing devices in said second and saidthird circuits respectively, said timing devices being mechanicallyinterconnected for simultaneous adjustment whereby the impulse of saidthird circuit can be adjusted to be coincident in time with any one ofthe pulses generated in said second circuit.

2. In a time interval measuring system, the combination of a highfrequency oscillatory device adapted to be electricall shock excitedinto oscillation and rapidly quenched, and a control pulse operatedelectrical timing circuit cooperatively connected to said device, saidcircuit including a timing portion having a time constant substantiallyexceeding in duration the period of the control pulse, said circuitproviding to said device an electrical shock excitation upon the receiptof an electrical control pulse by said circuit, said circuitautomatically quenching said oscillatory device by electricallyshort-circuiting the same at a predetermined time interval thereafter.

3. In a time interval measuring system, the combination of a highfrequency oscillation generator adapted to be shock excited intooscillation and rapidly quenched, said generator providing uponexcitation an oscillatory electrical wave of a substantially constanthigh frequency, a continuously adjustable phase shifting electricalnetwork electrically connected to the electrical output circuit of saidoscillation generator, a pulse generator electrically connected to theoutput of said adjustable phase shifting network and adapted to producea sharp impulse at a particular point of each cycle of the highfrequency wave, a first electrical circuit connected to said pulsegenerator and normally non-responsive to the pulses therefrom, a secondelectrical circuit connected to said first circuit and providingimpulses which render said first circuit responsive to pulses from saidpulse generator, said second circuit including an adjustable elec tricaltiming circuit controlling the timing of the impulses of said secondcircuit, and a mechanical linkage coupling the adjustment mechanisms ofsaid phase shifter and said electrical timing circuit whereby particularpulses of said pulse generator will be translated through said firstcircuit and may be employed to produce fiducial marks of accuratelyknown time relation with respect to the instant of shock excitation ofsaid high frequency generator, said combination further including astart-stop circuit responsive to electrical pulses and electricallyconnected to said high frequency generator and said second circuitfrequency generator and to quench it after a predetermined interval andto energize said second circuit to initiate the formation process of animpulse by said second circuit.

4. In a time interval measuring system, the combination of a highfrequency oscillation circuit adapted for shock excitation andsubstantially instantaneous quenching, means for shock exciting saidoscillation circuit, a continuously adjustable phase shifting circuitconnected to the output of said oscillation circuit, a pulse generatorconnected to the output of said phase shifting circuit, means forsegregating a particular one of the pulses generated by said pulsegenerator, and means for instantaneously quenching said oscillationcircuit to restore it to a quiescent state.

5. The combination of claim 4, said pulse selecting means including atiming circuit continuously adjustable over the interval of oscillationof the oscillation circuit, and a mechanical linkage coupling saidadjustable timing circuit with the adjustable phase shifting circuit ofclaim 4 whereby the segregation of a pulse can be effected at any pointof time within the interval of oscillation of the oscillation circuit.

6. In a pulse reflection object locating system a timing circuit forfacilitating the determination of the reflection time of pulses,comprising an oscillatory low-loss tuned circuit, a control circuitadapted and connected to suddenly vary the current flow through saidoscillatory circuit to produce free oscillation thereof, a circuitconnected to said oscillatory circuit, providing precisely timed pulsesfrom the oscillatory wave resulting from the free oscillation of saidtuned circuit, an auxiliary circuit providing a pedestal pulse at asubharmonic frequency of the free period of oscillation of said tunedcircuit, a phase shifter in the circuit of the precisely timed impulses,a second phase shifter in the auxiliary circuit providing the pedestalpulse, reduction gears coupling said two phase shifters whereby to shockexcite said high the pedestal pulseis shifted in phase only inproportion to the inverse of the harmonic ratio with respect to thephase shift imparted tosaid precisely timed pulses and a particular oneof the series of precisely timed pulses is selected as a fiducial markby combining the particular precise pulse With the pedestal pulse andpassing the combined wave through a vacuum tube amplifier biased toexclude pulses which have not been combined with the pedestal.

'7. In a distance measuring system Of the type in which energy pulsesare aperiodically emitted, reflections thereof are received, and thetime interval between the emission of pulses and the receipt ofreflections of said pulses from a particular object is determined bysynchronizing therewith auxiliary pulses derived from the control sourceof the emitted pulses the synchronization being effected byappropriately shifting the time base of the said auxiliary pulses, themethod of obtaining auxiliary pulses of like aperiodicity and ofincreasing the accuracy with which the time base adjustment of theauxiliary pulses can be determined which comprises deriving from thecontrol source of the emitted pulses a like series of pulses, shockexciting thereby into free oscillation, a precision low-loss oscillatorydevice, the free oscillation period of which is extremely short withrespect to the average interval between the pulses derived from thecontrol source, obtaining simultaneously a relatively low frequency 7cyclic wave having a period of substantially the same order as theaverage interpulse period of the pulses of said control source,simultaneously shifting the phases of the wave from the shock excitedhigh frequency source and the low frequency source, the phase shiftimparted to the first said wave being always greater than that impartedto the second said wave by the ratio of their respective periodicities,deriving from the high frequency oscillation a series of precisely timedsharp pulses, deriving from the low frequency cyclic wave a pedestalpulse at a particular selectable point in said low frequency wave, thewidth of the pedestal pulse being less than the separation betweenconsecutive high frequency pulses obtained from said high frequencyoscillation source, combining the high frequency pulses With thepedestal pulse, selecting only that high frequency pulse which iscoexistent in time with the pedestal pulse and employing the pulse soselected as a finducial mark or timing pulse,

and quenching both the said high frequency oscillatory device and saidlow frequency cyclic wave to reestablish a quiescent state, prior to theoccurrence of the next successive pulse derived from the control source.

8. In a pulse-reflection object locating system of the type in whichpulses of wave energy are emitted from an observation point to impingeupon objects within a particular region, refiections of said pulses fromobjects Within said region are received at said observation point, andthe distances from said point to the objects from which reflections arereceived are determined by measuring the time intervals required forpulses to be transmitted to and reflected back from said objects,respectively, the measurements being effected by synchronizing with thereflected pulses, auxiliary pulses derived in known time relation withrespect to the emitted pulses and delayed in time until the saidsynchronous relation with particular received reflected pulses has beenestablished, the method of deriving accurately timed and readilycontroliable auxiliary timing pulses which comprises shock exciting intofree oscillation in knowntime relation with respect to the emitted pulsea high frequency low-loss oscillator, deriving a first sine wavetherefrom, simultaneously shock exciting into free oscillation, a lowerfrequency low-loss oscillator having a period approximatelycommensurable with the average interpulse interval'between transmittedpulses and deriving a second sine Wave therefrom, shifting the phases ofsaid first and said second sine waves respectively, constraining thephase shift of said first wave to vary with that of said second wave inproportion to the frequency ratio ofsaid high to said lower frequencyWaves, deriving a series of sharp pulses from said phase-shifted highfrequency sine wave, deriving a pedestal pulse from said phase-shiftedlower frequency wave, combining the said sharppulses and the saidpedestal pulse, selecting the sharp pulse which coincides in time withsaid pedestal pulse and adjusting the said phase shifts until theselected sharp pulse coincides in time with a particular receivedreflected pulse and quenching both said oscillators prior to theemission of the next successive pulse, whereby the reflection timeinterval for said particular received reflected pulse can be accuratelydetermined.

9. In a pulse-reflection type of object detecting system, which includesa source of energy pulses, the pulses from said source occurringaperiodically, the interval between any two successive pulses being inexcess of a predetermined minimum time interval, a timing circuitproviding an auxiliary pulse occurring an accurately determinableadjustable time interval after each pulse from said source, said timingcircuit comprising a high frequency low-loss oscillatory device capableof shock-excitation into free oscillation and rapid quenching, anexciting and quenching circuit interconnected between said source ofenergy pulses and said oscillatory device, said last stated circuitshock exciting said oscillatory device upon the receipt of an impulsefrom said source and quenching it within the said predetermined minimumtime interval, a low frequency low-loss oscillatory device capable ofshock excitation into free oscillation and rapid quenching the period ofoscillation of said latter device being of the same order of magnitudeas said predetermined minimum time interval, the said exciting andquenching circuit being interconnected between said source of energypulses and said low frequency oscillatory device, said last statedcircuit shock exciting said last stated device upon receipt of animpulse from said source and quenching it within said predeterminedminimum time interval, said oscillatory devices providing, whenoscillating, high frequency and low frequency sine waves, respectively,a first accurately calibrated continuously adjustable phase shifterconnected to the output of said high frequency oscillatory device, asecond like phase shifter connected to the output of said low frequencyoscillatory device, a mechanical linkage coupling the adjustmentmechanisms of said two phase shifters, said linkage reducing theadjustment imparted to the mechanism of the said second phase shifter bythe frequency ratio of the high to the low frequency in actuating theadjustment mechanism of the said first phase shifter, a pulse generatoroperated by the high frequency wave output of said first phase shifterproducing a series of sharp accurately timed-pulses, a pedestalgenerator operated by the low frequency wave output of said second phaseshifter producing a pedestal pulse at a predetermined location withrespect to said phase shifted low frequency Wave and a fiducial markgenerator operated by the combined outputs of said pulse generator andsaid pedestal generator to produce a precisely timed fiducial mark orimpulse.

10. A circuit for accurately timing the receipt of reflections ofaperiodically recurrent emitted energy pulses comprising a highfrequency lowloss oscillatory sine Wave generator, a start-stop deviceoperatively connecting to said generator to instantaneously excite saidgenerator into scillation and to quench its oscillations abruptly at theend of a predetermined time interval, said time interval being at leastequal to the maximum reflection time to be measured, a continuouslyadjustable phase shifter operatively connecting to the output of saidsine wave generator, a pulse generator operatively connected to theoutput of said phase shifter, a pedestal pulse generator, a controlcircuit for said last-mentioned generator adjustable to operate saidpedestal pulse generator at any time Within the startstop intervaldefined by said start-stop circuit and operatively connecting thereto, acoupling mechanism coupling the adjustment mechanism of said last statedcontrol circuit with the adjustment mechanism of said continuouslyadjustable phase shifter, the coupling mechanism constraining adjustmentof said pedestal pulse to correspond in time delay with the phaseadjustment of said sine wave by said phase shifter and a fiducial markgenerator operatively connected with the combined outputs of said pulseand said pedestal generators to produce a fiducial mark precisely timedwith respect to the beginning of the interval of operation of saidstart-stop circuit.

STUART C. I-IIGHT.

REFERENCES- crrnn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,687,882 Nichols Oct. 16, 19282,181,568 Kotowski et a1 Nov. 28, 1939 2,354,086 MacKay July 18, 1944

